1. Technical Field
This invention relates to pigs for travelling through pipelines through which fluid flows or is intended to flow in order to carry out inspection, cleaning and other maintenance.
2. Background Information
Pipeline pigs in general are well known in the art, and many different configurations thereof are in use and an even higher number of configurations has been proposed. A general characteristic of known pigs is the requirement for an umbilical cord. Such a cord is typically used on one hand to supply power to the pig and to control its movement and may also be used on the other hand to return data to the operator e.g. a visual picture of the inside of the pipe.
For ongoing maintenance once a pipeline has been commissioned, it is usually impractical to halt the flow of fluid through the pipe and so it is normally necessary for the pig to operate while the fluid is flowing. Whilst advantage may be taken of this in one direction of the pig's travel, e.g. to deploy the pig, by allowing it to be carried along by the fluid flow; when it is required that the pig travels in the other direction, it is necessary to drive the pig against the flow. This is normally achieved by providing the pig with a motor which is powerful enough to drive it against the forward pressure of the flowing fluid.
The option of providing batteries on the pig to power such a motor would almost always be impractical due to their weight and the amount of power which would be needed.
It is an aim of the present invention to provide an improved pig and when viewed from a first aspect, the invention provides a device for travelling along a pipeline having fluid flowing along it, said device comprising means for extracting power from said fluid flow and using said power to move the device along the pipeline against the fluid flow.